In optical networks, optical signals become weaker and distorted after having travelled through a significant distance. Indeed, optical signals are degraded while propagating in the optical medium due to physical effects. Physical degradations depend on a plurality of factors, such as the distance to propagate over, the characteristics of the optical links, the frequency occupation, etc.
Numerical methods as for example Split Step Fourier Method (SSFM) are able to perform propagation calculations. In E. Seve et al., “Semi-Analytical Model for the Performance Estimation of 100 Gb/s PDM Transmission Systems without Inline Dispersion Compensation and Mixed Fiber Types,” Proc. ECOC, Th.1.D.2, London (2013), a semi-analytical model is described, that allows to determine the signal-to-nonlinear distortion ratio (SNRNL), which is an indicator of the performance of the transmission. The disclosed model is especially suitable for optical links having long lengths, for example above 100 km.